Datasheet

7
®
INA154
APPLICATIONS INFORMATION
Figure 1 shows the basic connections required for operation
of the INA154. Decoupling capacitors are strongly recom-
mended in applications with noisy or high impedance power
supplies. The capacitors should be placed close to the
device pins as shown in Figure 1.
As shown in Figure 1, the output is referred to the reference
terminal (pin 1). A voltage applied to this pin will be
summed with output signal. The differential input signal is
connected to pins 2 and 3. The source impedances con-
nected to the pinouts must be nearly equal to assure good
common-mode rejection. A 5Ω mismatch in source imped-
ance will degrade the common-mode rejection of a typical
device to approximately 80dB (a 10Ω mismatch degrades
CMR to 74dB). If the source has a known impedance
mismatch, an additional resistor in series with the opposite
input can be used to preserve good common-mode rejection.
Do not interchange pins 1 and 3 or pins 2 and 5, even though
nominal resistor values are equal. The resistors are laser
trimmed for precise resistor ratios to achieve accurate gain
and highest CMR. Interchanging these pins would not
provide specified performance.
OPERATING VOLTAGE
The INA154 operates from ±4V to ±18V supplies with
excellent performance. Most behavior remains unchanged
throughout the full operating voltage range. Parameters
which vary significantly with operating voltage are shown
in the Typical Performance Curves.
INPUT VOLTAGE RANGE
The INA154 can accurately measure differential signals
that are beyond the positive or negative power supply rails.
The linear common-mode range extends from 2•(V+) – 5V
to 2•(V–) +5V. See the Typical Performance Curve, “Input
Common-Mode Range vs Output Voltage.”
OFFSET VOLTAGE TRIM
The INA154 is laser trimmed for low offset voltage and
drift. Most applications require no external offset adjust-
ment. Figure 2 shows an optional circuit for trimming the
output offset voltage. The output is referred to the output
reference terminal (pin 1), which is normally grounded. A
voltage applied to the Ref terminal will be summed with the
output signal. This can be used to null offset voltage as
shown in Figure 2. The source impedance of a signal
applied to the Ref terminal should be less than 10Ω to
maintain good common-mode rejection.
FIGURE 1. Basic Power Supply and Signal Connections.
V
3
5
6
3
V
O
INA154
V
O
= V
3
– V
2
Offset Adjustment
Range = ±1V
2
R
3
R
1
R
2
R
4
V
2
10
Ω
150k
Ω
10
Ω
100k
Ω
+15V
–15V
1
FIGURE 2. Offset Adjustment.
V
3
5
6
3
INA154
V
OUT
= V
3
– V
2
2
Ref
R
1
25kΩ
R
3
25kΩ
R
2
25kΩ
R
4
V
2
25kΩ
R
L
1µF
V–
4
1µF
V+
7
1